1. Field of the Invention
The present invention relates to a longitudinally coupled resonator-type surface acoustic wave filter that uses shear horizontal (SH) waves.
2. Description of the Related Art
In related art, surface acoustic wave devices are widely used for applications such as resonators and bandpass filters. International Publication No. 2012/086639 discloses an elastic wave device using SH waves. This elastic wave device includes a high acoustic velocity layer, a low acoustic velocity film, a piezoelectric film, and an interdigital transducer (IDT) electrode stacked in the stated order over a support substrate. The ability of this device to confine the energy of SH waves is supposed to provide an increased Q factor.
In the elastic wave device described in International Publication No. 2012/086639, not only SH waves but also Rayleigh waves (P+SV waves) are confined. Thus, fabricating a longitudinally coupled resonator-type surface acoustic wave filter by using the stacked structure described in International Publication No. 2012/086639 leads to the appearance of large spurious responses caused by Rayleigh waves.